Heat shield arrangements for reprographic apparatus



- March 24, 1970 L. F. WJLAWES ET A ,50

I HEAT SHIELD ARRANGEMENTS FOR REPROGRAPHIC APPARATUS Filed May 12, 1966 2 Sheets-Sheet 1' FIG3 | F. w. LAWES ET AL 3,502,844

March 24, 1970 HEAT SHIELD ARRANGEMENTS FOR REPROGRAPHIC APPARATUS I 2 Sheets-Sheet 2 Filed May 12, 1966- mm mm B United States Patent US. Cl. 219-343 4 Claims ABSTRACT OF THE DISCLOSURE In a reprographic-apparatus image-fusing device comprising a radiant heat source and a support plate for supporting an image-carrying sheet during transport thereof past said source to fuse and fix such image, a backing shield is provided behind the reflector and spaced therefrom and air blowing means is arranged to supply air to and through such space thereby to minimize transfer of heat to the backing shield. The air blowing means also supplies air to and through a space between the source and the support plate, and selectively actuated damper means is provided for blocking the flow of air to this latter space while permitting air to flow through the space between the reflector and the backing shield. Preferably a further plate is provided, spaced from the support plate on the side thereof remote from the source, and this further plate and the backing shield are provided, on their sides remote from the support plate and the reflector respectively, with respective layers ,of thermally insulating material, which may be expanded polystyrene.

This invention relates to reprographic apparatus, and more particularly to arrangements in such apparatus for shielding parts thereof from heat generated by a radiant energy source comprised by the apparatus.

One of the problems associated with reprographic apparatus arises from the generation of unwanted heat from light and heat sources, one or both of which are commonly required in such apparatus. This problem becomes particularly acute in small machines, in which not only are the sources necessarily positioned close to other parts of the machine but also very limited space is available in which to locate mechanical means, such as fans, for dissipating unwanted heat. If an undesirable heat build up occurs there can, for instance, be serious interference with the performance of the recording medium, usually a fusible powder; or actual scorching of paper or like material employed may result.

It is an object of this invention to provide simple and compact means for overcoming these difficulties.

According to the invention a radiant energy source in or for reprographic apparatus is provided with a reflector and there is further povided, behind and spaced from the reflector, a backing shield such that there is a heatinsulating air gap between the reflector and the backing shield.

Preferably, the reflector and the backing shield are of materials, such as aluminium, which are good conductors of heat.

Preferably also, the external face of the backing shield is provided with a layer of heat-insulating material such as expanded polystyrene.

Further according to the invention, there may also be associated with the combination of radiant energy source, reflector and backing shield, referred to above, a support plate disposed to be illuminated or heated by the source 3,502,844 Patented Mar. 24, 1970 and adapted to support a web or sheet of paper or like material to be so illuminated or heated, the support plate being of heat-conductive material and having on its back Surface a layer of heat-insulating material.

Means may, according to the invention, be provided whereby a flow of cooling air can be directed over the light or heat source and the reflector, through the air gap between the reflector and its backing shield, and, when a support plate is provided, over the support plate. Means may also be provided to select and control the said airflow.

The invention will be more fully understood from the following description of embodiments thereof with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic cross-sectional view of a light source combined, in accordance with the invention, with a reflector and a backing shield;

FIGURE 2 is a diagrammatic vertical cross section showing parts, including the light source combination shown in FIGURE 1, of a reprographic machine, and

FIGURE 3 is a diagramatic longitudinal vertical section showing parts of the reprographic machine which are shown in FIGURE 2.

In reprographic apparatus, light sources are used for a wide range of purposes and in particular for the projection of images on to light sensitive surfaces. Because such light sensitive surfaces generally need a considerable amount of light, and because reprographic apparatus is required to be swift in operation, the wattages employed are generally fairly high, and consequently a large amount of incidental and unwanted heat is generated. In order to increase the efflcient utilisation of the light available, light sources are generally supplied with a reflector. In FIGURE 1, there is shown a thin tubular light source I mounted on a reflector 2, but it will be understood that the invention may be applied to light sources of any other suitable shape, the reflector being then designed to the shape of the source and not necessarily being of the shape illustrated. Sockets or holding contacts 3 which support the source 1 are mounted directly on to the reflector 2. Substantially parallel to the reflector, and behind it but spaced from it by a narrow air gap, is a backing shield 4, on which the reflector is mounted by studs 5. These studs are preferably of a non-heat-conductive material such as ceramic, although the amount of heat transmitted by conduction along such support studs would often be sufficiently small to allow the use of heat conductive materials. In a slightly modified arrangement, the support studs studs 5 and light supports 3 might be combined as composite support members supporting both the reflector 2 and the source 1; or suitable apertures might be provided in the reflector to enable the light source to be mounted directly on the backing shield 4 so that the reflector need support no weight.

The reflector 2 and backing shield 4 are constructed of a material which is a good conductor of heat. A particularly suitable material for the purpose is aluminium, which is also capable providing an excellent mirror-like reflective surface. The air gap between the reflector and shield can be selected at choice, although it is usually not very large, because of the need to conserve space, and because only a narrow gap is needed to provide a highly eflicient heat insulation between the adjacent surfaces of the reflector and the backing shield. In order to reduce still further unwanted heating efiiects, the external surface of the backing shield is covered with a layer 6 of heat insulating material. Expanded polystyrene in thin sheet form is found to be particularly effective for this purpose, where the curvature of the backing shield is in one plane only, since it readily conforms to the contour of said backing shield. Some care must be exercised in selection of adhesive to aflix the expanded polystyrene to the backing shield, since the temperature attained can affect the adhesive qualities of the adhesive, or cause it to attack the insulating layer, while some adhesives themselves attack the insulating layer even in a cold condition; but suitable adhesives for the purpose are known and widely available.

In a construction according to FIGURE 1, the mirror reflects the greater part of the heat incident on it while the light source is switched on, but some radiant energy is absorbed by the mirror which thus heats up. Because of the high thermal insulation value of air, very little of this absorbed heat is transmitted to the backing shield; and, particularly if a flow of air is provided through the air gap so that the air temperature is kept to a minimum, the backing shield loses such heat as is transmitted to it almost entirely to the air in the gap and scarcely at all by conduction through the insulating layer 7 to other parts of apparatus in which the source 1 and other elements shown in FIGURE 1 are installed.

The light source combination shown in FIGURE 1 is incorporated in a reprographic machine of which parts are shown in FIGURES 2 and 3.

In FIGURE 2, 11 is a front wall of the illustrated machine and is formed with an aperture 12, provided with a feed table 13, for feeding into the machine an original document which is to be copied. Aligned with the feed table 13 is the upper run of an endless band 14 which is supported by rollers 15 and 16 of which at least one is driven by a main drive of the machine whenever the machine is switched on. Four pinch rollers 17, 18, 19 and 20 are pressed into engagement with the band 14 by spring means (not shown) so as to rotate therewith. Thus a document fed into the machine through the aperture 12 enters the nip between the band 14 and roller 17 and is there gripped to be fed, with the band, until its leading edge is gripped in turn between the band 14 and the rollers 18, .19 and 20, whereafter the document is fed out of the machine through an aperture 21 in the front wall 11. A fixed curved guide 22 guides the leading edge of the document from the roller 18 to the roller 19, and a further fixed guide 23 supports the leading edge of the document as it is advanced from the roller 19 to the roller 20.

As the document is inserted through the aperture 12 and advanced by the band 14, it trips each in turn of five microswitches MSl, MS2, M83, M84 and M85, which are included in circuitry (not shown) comprised by the machine and controlling the initiation and performance of the various operations which it performs in making a copy.

As the document to be copied is inserted through the aperture 12, the microswitch M81 is closed to energise a relay (not shown) which energises the light source 1 which illuminates the document as it passes between the roller 17 and the microswitch MS2. This latter switch is in parallel with the switch M81 and keeps the light source 1 energised until the trailing edge of the document passes the microswitch MS2, when the light source 1 is switched off again. While the light source 1 is energised, the illuminated part of the moving document is imaged, by an optical system (not shown), on the moving surface of a light-sensitive drum (not shown) of the machine, the drum being driven at appropriate speed by the main drive of the machine. In known manner, each part of the drum surface is electrostatically charged, prior to having a part of the document imaged on it, by means not shown; and the incidence of the light image causes the drum to record an electrostatic image of the document. When the leading edge of the document trips the microswitch MS3, at the appropriate time as determined by the position of this switch relative to the band 14, a solenoid (not shown) becomes energised and opens a shutter of a toner or developer unit (not shown) of the machine, to allow developer therefrom to cascade over the drum surface;

the solenoid remains energised until the trailing edge of the document passes the switch M83, and developer accordingly cascades over at least a corresponding peripheral length of the moving drum, to develop the whole of the electrostatic image of the document.

Tripping of the switch M83, and subsequent tripping of the switch MS4 when the leading edge of the document being copied reaches it, together result in actuation of a copy-paper feed mechanism (not shown) which advances a sheet of copy paper from a stack (not shown) into engagement with copy-paper transport means (not shown) which transports the sheet of copy paper to the drum for transfer, in known manner, of the developed image from the drum to the copy paper. The copy-paper feed mechanism is only required to act for a short time (until the sheet of copy paper is engaged by the copy-paper transport means), and becomes deenergised when the trailing edge of the document being copied passes the switch M83.

The copy paper, to which the developed image is transferred, is stripped from the drum and fed along a guide or chute 32 to the nips between a roller 33 driven by the main drive of the machine and a pair of rollers 34 c0- operating with opposite ends of the roller 33 so as to engage the edges of the copy paper and feed it, without touching the part of its upper surface which carries the transferred image, to a heater unit 35 which, like the above-described light-source combination, is in accordance with the present invention. The guide 32 comprises a flat supporting plate 36, on which the copy paper slides, and lateral guide strips 37 slightly spaced above the edges of the plate 36 and overlying the edges of the copy paper there-on so as to maintain the copy paper flat without touchingthe part of the upper surface thereof on to which the developed image has been transferred.

The heater unit 35, shown in FIGURES 2 and 3, comprises a support plate 38 on which the copy paper slides as it is advanced by the rollers 33 and 34, lateral guide strips 39 similar to the guide. strips 37 of the chute 32, and serving a similar purpose, and an upper reflector 40 on which are mounted four heater elements 41. The plate 38 is stiffened by bars 42 to minimise any tendency to buckling under the effect of heat, and an underplate 43'is provided with a layer 44 of heat-insulating material. Spaced above the reflector 40 is a backing shield 45 which is similarly provided with a layer 46 of heat insulating material. The ends of the reflector 40, to which the ends of the guide strips 39 are secured, are stiffened by bars 47 which also serve to locate the backing shield 45 and the insulating layer 46 thereon. At the exit end of the heater unit, the reflector 40 is fitted with tines 48 extending obliquely upwardly to flatten the advancing leading edge of the copy paper if this should have become buckled by heat during its passage through the heater unit. As the copy paper, advanced by the rollers 33 and 34, emerges from the heater unit its leading edge enters the nip between a pair of rollers 49 and 50, of which one is driven 'by the main drive of the machine, and these feed the copy paper out of the machine through an aperture 51 in the front wall 11 thereof.

The electrical connections of the four heater elements 41 of the heater unit are not shown, but suitably they may be connected in pairs in series, with the two pairs in parallel with ane another.

Conveniently, each of the elements 41 is an infra-red heater element which would deliver 850 watts if connected individually across the mains supply. Thus the four elements, connected as illustrated, together deliver about 850 watts; but they constitute a more widely distributed source. of heat than a single element would do, and each is operating at lower temperature than normal and is therefore delivering relatively more infra-red radiation and relatively less visible light.

The machine also includes a -fan 27, which supplies cooling air which is fed through a branched duct 57 (see FIGURE 2) partly through a branch 57a to the vicinity of the light source 1, to prevent it from becoming overheated, and partly through a branch 57b to one side of the heater unit through which the air then passes transversely to be discharged at the other side. Entry of the air into the heater unit is controlled by means of a butterfly valve 58 actuated by a solenoid52. When closed, the valve 58, shaped as a major segment of a circle, shuts off the supply of air to the space between the reflector 40 and the support plate 39; but the remaining minor segment of the circular-section part of the branch 57b in which the valve 58 is located remains permanently open to supply air at all times to the space between the reflector 40 and the backing shield 45. To ensure the separation of these air supplies there is provided within the branch 57b a dividing plate 58', alignedwith the reflector 40, with which dividing plate the upper edge of the valve 58 co-operates when closed. The valve 58 is provided with a crank 59, the end of which engages in a slot 60 in a weighted rod 61 pivotally carried by the armature of the solenoid 52. The valve 58 is normally open but closes when the solenoid is energised, to cut oil? the supply of air to the main space within the heater unit. The solenoid is energised, under control of the controlling circuitry of the machine, to close the valve 58 While a sheet of copy paper is passing through the heater unit. At such times, "the passage of the paper itself provides a cooling effect; and furthermore it is desirable to avoid any risk of the copy paper being disturbed, and perhaps displaced, by cooling air blowing over it.

Preferably, the sequence timing provided by the control circuitry of the machine is such that energisation of the heater elements 41 begins some time before a sheet of copy paper reaches the heater unit. This results in the support plate 38 being preheated. This preheating of the support plate 38 of the heater unit to an adequate initial temperature not only minimises the tendency of the copy paper to curl or buckle due to dilferential heating on its two sides but also ensures that moisture expelled from successive sheets of copy paper as they are heated will not condense and collect on the support plate. Such collected moisture would tend to prevent later sheets of copy paper coming in contact with it from being evenly heated to a suflicient temperature to fix the image which they carry, and this could lead to incomplete or patchy fixing of such images. To improve this preheating effect, it is found preferable to make the upper surface of the support plate 38, which is exposed to radiation from the heating elements 41, non-reflective and dark in colourso that it absorbs a considerable part of the radiation incident on it.

What we claim is:

1. Reprographic-apparatus image-fusing means comprising a radiant heat source, a reflector in the form of a sheet disposed with the said source on one side thereof, a backing shield in the form of a sheet disposed adjacent the said reflector on the other side thereof and in spaced relationship therefrom, a support plate disposed, with the said source between it and the reflector, to support an imagecarrying sheet during transport thereof past said source to fuse and fix such image, air blowing means arranged to supply air to and through the spaces between the reflector and the backing shield, thereby to minimize transfer of heat to the backing shield, and respectively, between the reflector and the support plate, and selectively actuated means for blocking the flow of air to the space between the reflector and the support plate while permitting air to flow through the space between the reflector and the backing shield.

2. Reprographic-apparatus image-fushing means as claimed in claim 1 comprising a further plate spaced from.

said support plate on the side thereof remote from said source, and a layer of thermally insulating material on the side of said further plate remote from said support plate.

3. Reprographic-apparatus image-fusing means as claimed in claim 2 comprising stiffening bars secured to said support plate and having secured to them said further plate.

4. Reprographic-apparatus image-fusing means as claimed in claim 1, comprising a layer of thermally insulating material provided on the side of said backing shield remote from said reflector.

References Cited UNITED STATES PATENTS 2,260,803 10/1941 Dewar 219347 X 2,332,099 10/1943 McKinnis.

2,963,565 12/ 1960 Moore et al.

2,965,868 12/1960 Eichler.

3,159,735 12/1964 Eisner et al. 2l9347 3,171,945 4/1965 M eng et al. 219-447 FOREIGN PATENTS 572,911 10/1945 Great Britain.

ANTHONY BARTIS, Primary Examiner US. Cl. X.R. 

